Joints of human fingers are the most important parts of an upper extremity for gripping an article, and are most fundamental hinge joints, and it is said that when function of the finger joint is damaged, almost all functions of the upper extremity will be lost, and accordingly, the finger joints are very important parts of a human fingers for gripping an article.
A basic structure of the fingers will be explained with reference to structures of second to fifth fingers (i.e., forefinger, long finger, annular finger and little finger). As shown in FIG. 6 showing a bone structure of a human hand, fingers of a human has, from its root side, a metacarpal phalanx 10, proximal phalanx 12, a middle phalanx 14, and a distal phalanx 16 in the described order, and finger joints as jointing portions of these phalanxes are composed, respectively of a metacarpal proximal segment joint 11 (called MP joint, hereinlater), a proximal middle segment joint 13 (called PIP joint, hereinlater), and a middle distal segment joint 15 (called DIP joint, hereinlater). A part of the metacarpal born is called metacarpus 20, a part of the proximal phalanx 12 is called proximal segment 22, a part of the middle phalanx 14 is called middle segment 24, and a part of the distal phalanx 16 is called distal segment 26.
Since the structure of the finger is very complicated, its movement is also complicated. For example, although the MP joint 11 of the root portion of the finger can be moved independently alone, the PIP joint 13 and the DIP joint 15 disposed on the front side of the MP joint are moved in association with each other. That is, when a finger is bent in an unintentional natural manner, the PIP joint 13 is first bent and the DIP joint 15 is thereby bent. Accordingly, the human finger the proximal segment 22, the middle segment 24 and the distal segment 26 are entirely integrally bent with the MP joint 11 being fulcrum, and on the other hand, the proximal segment 22, the middle segment 24 and the distal segment 26 are bent with the PIP joint 13 and DIP joint 15 being fulcrums, respectively. Such movements of the finger will be realized in association with complicated movement of muscles.
Incidentally, it is conventionally required to reproduce human fingers, which have complicated structures and are operated complicated manner, as a robot, and to have the robot to do various workings in place of the human fingers. If such robot as is provided with the functions of the human fingers is utilized for the workings at an undesirable environment having high temperature and high humidity, or a portion in which radiation is radiated, and in a specific environment such as outer space, working efficiency, safety working environment or like can be improved as well as reduction of running cost. In consideration of such circumstances, various joint structures of robots have been proposed.
For example, Patent Publication 1, mentioned hereinafter, discloses a robot in which rotation shafts of motor driving arms are provided in parallel with a central axis of swing motion of the arms. In this joint structure, a joint portion is constructed by supporting, to be swingable, a second arm to the front end portion of a first arm, the motor is disposed on the central axis of the swing motion at this joint portion, and rotating motion of the motor is transmitted to the first or second arm through a reduction mechanism including a spa gear and so on to thereby apply the swing motion in response to the rotating direction and rotating amount of the motor to these arms.
In addition, Patent Publications 2 and 3, mentioned hereinafter, disclose structures in which first and second arms are connected to be swingable by means of a link mechanism, and the first arm is swung with respect to the second arm by using a ball screw to a portion of such link mechanism and rotating the ball screw by driving the motor. For example, in a joint structure disclosed in the Patent Publication 2, the second arm is supported to be swingable with respect to the first arm, but the second arm is provided with a screw shaft in parallel with the second arm, and the screw shaft is rotated by driving the motor mounted to the second arm. In addition, a nut member is screwed with the screw shaft mentioned above, and an end portion of a link plate extending from the first arm is jointed to the nut member to be rotatable. According to this structure, when the motor is driven, the nut member is moved on the screw shaft in accordance with the rotating amount and the rotating direction of the motor. However, since the end portion of the link plate is jointed to this nut member, pushing or pulling force in response to the movement of the nut member acts to the second arm from the link plate, whereby the second arm causes the swing motion with respect to the first arm.
Patent Publication 1: Japanese Unexamined Patent Application Publication No. HEI 05-092377
Patent Publication 2: Japanese Unexamined Patent Application Publication No. HEI 10-217158
Patent Publication 3: Japanese Unexamined Patent Application Publication No. 2002-113681